Block copolymer composition

ABSTRACT

A heat stabilized block copolymer composition which comprises a block copolymer comprising a polymer block mainly composed of a monoalkenyl aromatic compound and a polymer block mainly composed of a conjugated diene compound, the content of the monoalkenyl aromatic compound being 5-95% by weight based on the total weight of the block copolymer, and phenolic stabilizers. By adding two or more specific phenolic stabilizers to a block copolymer of a monoalkenyl aromatic compound and a conjugated diene compound, there can be obtained a block copolymer composition which exhibits excellent heat stability even under being heated at high temperatures, is high in the effect of being inhibited from formation of gel-like materials and is excellent in color tone.

This application is the national phase under 35 U.S.C. §371 of PCTInternational Application No. PCT/JP01/01317 which has an Internationalfiling date of Feb. 22, 2001, which designated the United States ofAmerica and was not published in English.

TECHNICAL FIELD

The present invention relates to a block copolymer composition excellentin heat stability and color fastness which comprises a block copolymercomprising a specific monoalkenyl aromatic compound and a specificconjugated diene compound and a specific phenolic stabilizer.

BACKGROUND ART

Block copolymers comprising monoalkenyl aromatic compounds andconjugated diene compounds which have not been vulcanized have thesimilar elasticity to that of vulcanized natural rubbers or syntheticrubbers at room temperature if content of the monoalkenyl aromaticcompounds is relatively small and, besides, have the similarprocessability to that of thermoplastic resins at high temperatures,and, hence, they are widely utilized in the fields of footwear, plasticsmodification, asphalt, pressure sensitive adhesives, and others.

Furthermore, if content of the monoalkenyl aromatic compounds isrelatively large, transparent thermoplastic resins excellent in shockresistance are obtained. Therefore, recently, the block copolymersincrease in their usage mainly in the fields of food packagingcontainers and, moreover, their uses are being diversified into a widevariety of fields.

However, since the block copolymers comprising monoalkenyl aromaticcompounds and conjugated diene compounds have carbon—carbon double bondsin the molecules, they suffer from the problems that they are inferiorin heat stability and the effects to improve characteristics of theblock copolymers per se, for example, elastic characteristics, adhesionand impact resistance cannot be sufficiently exhibited. Accordingly, inorder to improve the heat stability of these block copolymers, therehave been used phenolic stabilizers, phosphorus stabilizers, sulfurstabilizers, and the like.

For example, BHT (2,6-di-tert-butyl-4-methylphenol) which is most widelyused must be used in a large amount because it has a relatively highoxidation inhibition function and a relatively high heat resistance, butis readily volatilized in case the molding temperature is high.Furthermore, when other phenolic stabilizers are used, they must be usedin a large amount for obtaining high heat stabilization effect, and,thus, in many cases, there is caused a problem that block copolymercompositions are colored in use at high temperatures or at the time ofmolding at high temperatures. On the other hand, when phosphorusstabilizers and/or sulfur stabilizers are used in combination withphenolic stabilizers, the heat stabilization effect is improved, butthere are problems of hydrolysis in the case of phosphorus stabilizersand odor development in the case of sulfur stabilizers.

In view of the above problems, the applicant proposed in JP-A-4-246454 atechnique of improving the heat stability of block copolymers by using,in combination, 0.005-0.05 part by weight of a specific sulfur phenolicstabilizer, 0.1-2.0 parts by weight of other specific phenolicstabilizer, and optionally a phosphorus stabilizer. However, it has beenfound that even this technique requires use of phosphorus stabilizers inactual use. However, since phosphorus stabilizers have the problem ofhydrolysis, there is a limit in heat stabilization effect in actual use,and the technique for improving heat stability of block copolymerswithout using phosphorus stabilizers is demanded.

As mentioned above, conventional stabilizers, whether they are usedsingly or in combination of two or more, have a limit in the effect toimprove heat stability of block copolymers of monoalkenyl aromaticcompounds and conjugated diene compounds, and, for some uses, productshaving sufficient heat stability cannot be obtained and block copolymercompositions having truly high heat stability performance have long beendemanded.

The present invention has been made for meeting the demand, and theobject is to solve the problems on heat stability performance in theconventional block copolymer compositions and provide block copolymercompositions which can exhibit excellent heat stability even under beingheated at high temperatures, are high in the effect to inhibitproduction of gel-like materials and excellent in color fastness andhave a satisfactory color tone.

DISCLOSURE OF INVENTION

As a result of intensive research conducted by the inventors in anattempt to solve the above problems, it has been found that a blockcopolymer composition comprising a block copolymer of a specificmonoalkenyl aromatic compound and a specific conjugated diene compoundand a specific phenolic stabilizer is excellent in heat stability,namely, is not deteriorated in properties even if it is heated at hightemperatures, can be inhibited from formation of gel-like materials, isexcellent in color fastness and has good color tone. Thus, the presentinvention has been accomplished.

That is, the present invention relates to a block copolymer compositionwhich comprises (a) a block copolymer comprising a polymer block segmentmainly composed of a monoalkenyl aromatic compound and a polymer blocksegment mainly composed of a conjugated diene compound, content of themonoalkenyl aromatic compound being 5-95% by weight based on the totalweight of the copolymer, (b) a phenolic stabilizer represented by thefollowing formula (I):

(wherein R₁ and R₃ are —CH₂—S—R₅ in which R₅ represents an alkyl groupof 1-18 carbon atoms, R₂ represents a hydrogen atom or a methyl group,and R₄ represents an alkyl group of 1-8 carbon atoms or a cycloalkylgroup of 5-12 carbon atoms), and (c) at least one phenolic stabilizerselected from the phenolic compounds represented by the followingformulas (II)-(V):

(wherein R₆ is represented by the following formula (VI):

R₇ represents an alkyl group of 2-22 carbon atoms, and R₈-R₁₂ eachrepresent a hydrogen atom or an alkyl group of 1-6 carbon atoms, with aproviso that two or more of R₈-R₁₂ are alkyl groups), content of thephenolic stabilizer (b) being more than 0.05 part by weight and lessthan 0.6 part by weight and that of the phenolic stabilizer (c) beingnot less than 0.05 part by weight and not more than 0.8 part by weightbased on 100 parts by weight of the block copolymer (a).

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be explained in detail below.

The block copolymer used in the present invention is a block copolymercomprising a polymer block segment mainly composed of a monoalkenylaromatic compound and a polymer block segment mainly composed of aconjugated diene compound. Furthermore, in the block copolymer of thepresent invention, content of the monoalkenyl aromatic compound is inthe range of 5-95% by weight based on the total weight of the blockcopolymer. In the present invention, said block copolymer may be usedsingly or in admixture of two or more.

Here, the polymer block segment which is mainly composed of amonoalkenyl aromatic compound and constitutes the block copolymer of thepresent invention is a homopolymer of the monoalkenyl aromatic compoundor a copolymer of the monoalkenyl aromatic compound and other monomerswhich contains more than 50% by weight of the monoalkenyl aromaticcompound and is substantially mainly composed of the monoalkenylaromatic compound.

The polymer block segment mainly composed of a conjugated diene compoundis a homopolymer of the conjugated diene compound or a copolymercomprising a monoalkenyl aromatic compound and the conjugated dienecompound and containing more than 50% by weight of the conjugated dienecompound. In such copolymer block, the monoalkenyl aromatic compound maybe distributed uniformly or ununiformly (for example, with a taper).Furthermore, in the block, there may coexist a plurality of the portionswhere the monoalkenyl aromatic compound is distributed uniformly and/orthe portions where the monoalkenyl aromatic compound is distributedununiformly.

In the block copolymer of the present invention, the content of themonoalkenyl aromatic compound must be in the range of 5-95% by weightbased on the total weight of the block copolymer. If the content of themonoalkenyl aromatic compound is less than 5% by weight, the blockcopolymer is inferior in mechanical properties such as tensile strengthwhich are preferable characteristics as thermoplastic elastic materials.On the other hand, if it exceeds 95% by weight, the block copolymer isinferior in mechanical strengths such as impact resistance which arepreferable characteristics as thermoplastic resins. The block copolymerof the present invention shows the characteristics as thermoplasticresins when the content of the monoalkenyl aromatic compound exceeds 60%by weight, preferably is not less than 65% by weight based on the totalweight of the block copolymer, and shows the characteristics asthermoplastic elastic materials when the content of the monoalkenylaromatic compound is not more than 60% by weight, preferably not morethan 55% by weight.

Especially, in the present invention, when the content of themonoalkenyl aromatic compound is not more than 60% by weight based onthe total weight of the copolymer, there is obtained a copolymer(thermoplastic elastic material) which is particularly high in theeffect of improvement in heat stability, is inhibited from formation ofgel-like materials under heating at high temperatures and is excellentin color fastness.

As examples of the monoalkenyl aromatic compound in the block copolymerconstituting the present invention, mention may be made of monomers suchas styrene, p-methylstyrene, tertiary butylstyrene, α-methylstyrene,1,1-diphenylethylene, and the like. Among them, styrene is preferred.These monomers may be used each alone or in combination of two or more.

As examples of the conjugated diene compound, mention may be made ofmonomers such as 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene,3-butyl-1,3-octadiene, phenyl-1,3-butadiene, and the like. Among them,1,3-butadiene and isoprene are preferred. These monomers may be usedeach alone or in combination of two or more.

The block copolymers used in the present invention are obtained by thegenerally employed consecutive polymerization method or the consecutivepolymerization method in combination with coupling reaction. Structuresof the copolymers can be various structures such as straight chainstructure, radial structure, star structure, branched structure, and thelike.

Typical examples are block copolymers represented by the formula:(A-B)_(n), (A-B)_(n)A or (B-A)_(n)B (wherein A is a polymer blocksegment mainly composed of monoalkenyl aromatic compound, B is a polymerblock segment mainly composed of conjugated diene compound, and n is aninteger of 1 or more).

Further examples are block copolymers represented by the formula:[(A-B)_(n)]_(m)-X, [(A-B)_(n)A]_(m)-X or [(B-A)_(n)B]_(m)-X (wherein Ais a polymer block segment mainly composed of monoalkenyl aromaticcompound, B is a polymer block segment mainly composed of conjugateddiene compound, n is an integer of 1 or more, m is an integer of 3 ormore, and X represents a residue of trifunctional or higher functionalcoupling agents or a residue of trifunctional or higher polyfunctionalorganolithium compounds). Examples of the trifunctional or higherfunctional coupling agents are silicon tetrachloride, tin tetrachloride,epoxy compounds such as epoxidized soybean oil, and the like,alkoxysilane compounds such as trimethoxysilane, tetramethoxysilane, andthe like, polyhalogenated hydrocarbon compounds, carboxy acid estercompounds, and the like.

Number average molecular weight, in terms of polystyrene, of the blockcopolymers used in the present invention is preferably 20,000-800,000,more preferably 30,000-700,000. If the number average molecular weightis less than 20,000, the mechanical property shown by tensile strengthor the like is deteriorated. If the number average molecular weight ismore than 800,000, viscosity is too high, and the block copolymer causesunsatisfactory dispersion and deterioration of processability in casethey are employed for the uses such as footwear and pressure sensitiveadhesives.

Method for producing the block copolymer constituting the presentinvention will be explained. First, in the case of obtaining, forexample, a block copolymer having the A-B-A structure shown bypolystyrene-polybutadiene-polystyrene, styrene is polymerized, thenbutadiene is polymerized and further styrene is polymerized in an inerthydrocarbon solvent using an organolithium compound as a polymerizationinitiator in an inert gas atmosphere such as nitrogen. When B in theA-B-A structure is a random copolymer block segment ofstyrene/butadiene, there may also be employed a method which comprisespolymerizing styrene and then charging styrene and butadiene together,followed by polymerizing them, a method which comprises simultaneouslypolymerizing styrene and a part of butadiene and then addingsupplemental butadiene, and the like.

The inert hydrocarbon solvents used for the production of the blockcopolymers of the present invention include, for example, cyclohexane,n-hexane, benzene, toluene, octane and mixtures thereof.

Furthermore, the organolithium compounds used for the production of theblock copolymers include, for example, ethyllithium, propyllithium,n-butyllithium, sec-butyllithium, tert-butyllithium, phenyllithium,propenyllithium, and hexyllithium, and the like which are knowncompounds. Among them, n-butyllithium and sec-butyllithium arepreferred. The organolithium compounds may be used each alone or inadmixture of two or more. Amount of the organolithium compounds isselected so that the block copolymers have a number average molecularweight in terms of standard polystyrene of 20,000-800,000.

When the segment B of the block copolymer represented by A-B-A structureis a random copolymer of a monoalkenyl aromatic compound and aconjugated diene compound, the chain distribution of the monoalkenylaromatic compound can be adjusted by adding a polar compound beforeinitiation of the polymerization and/or during the polymerizationreaction. As the polar compound, there are used, for example, ethers andtertiary amines, specifically, one or two or more compounds selectedfrom ethylene glycol dimethyl ether, tetrahydrofuran,α-methoxytetrahydrofuran, N,N,N′,N′-tetramethylethylenediamine, and thelike. Moreover, tertiary alkoxides of alkali metals can also be used.Examples of the tertiary alkoxides of alkali metals arepotassium-t-butoxide, potassium-t-amylalkoxides, sodium-amylalkoxides,potassium isopentyloxide, and the like.

Amount of vinyl linkage in the conjugated diene compound in the blockcopolymer constituting the present invention can also be optionallycontrolled depending on uses, but is preferably not more than 80 mol %.If the amount of vinyl linkage exceeds 80 mol %, elastic properties orlow-temperature characteristics of the block copolymer are sometimesinferior. More preferred amount of the vinyl linkage is not more than 70mol %. For the control of the amount of vinyl linkage in the conjugateddiene compound, there are used, for example, ethers and tertiary amines,specifically, one or two or more selected from ethylene glycol dimethylether, tetrahydrofuran, α-methoxy-tetrahydrofuran,N,N,N′,N′-tetramethylethylenediamine, and the like.

The phenolic stabilizer (b) used in the block copolymer composition ofthe present invention is represented by the formula (I) wheresubstituents R₁ and R₁ are shown by —CH₂—S—R₅ is an alkyl group of 1-18carbon atoms, R₂ is a hydrogen atom or a methyl group, and R₄ is analkyl group of 1-8 carbon atoms or a cycloalkyl group of 5-12 carbonatoms. When the substituent R₄ is other than methyl group, thesubstituent R₂ is preferably a methyl group.

R₅ is preferably an n-octyl group or an n-dodecyl group, and examples ofthe alkyl group of 1-8 carbon atoms in the substituent R₄ are methylgroup, ethyl group, n-butyl group, sec-butyl group and tert-butyl group,preferably methyl group and tert-butyl group. Examples of the cycloalkylgroup of 5-12 carbon atoms are cyclopentyl group, cyclohexyl group,cycloheptyl group, cyclooctyl group, and the like, preferably cyclohexylgroup.

The phenolic stabilizer (b) represented by the formula (I) must be addedin an amount of more than 0.05 part by weight based on 100 parts byweight of the block copolymer (a). If the amount of the phenolicstabilizer (b) is not more than 0.05 part by weight, sometimes thephenolic stabilizer (c) other than the phenolic stabilizer (b) must beused in a large amount for obtaining, for example, the effect to inhibitgelation in heating at high temperatures as in the present invention,and in this case the color fastness of the block copolymer compositionin heating at high temperatures sometimes deteriorates. Furthermore, ifthe amount of the phenolic stabilizer (b) is 0.6 part by weight or more,the block copolymer composition may be colored when it is heated at hightemperatures for a long time, and, hence, the upper limit is less than0.6 part by weight, and preferably not more than 0.3 part by weight.

Examples of the phenolic stabilizers represented by the formula (I) are2,4-bis(n-octylthiomethyl)-6-methylphenol,2,4-bis(n-dodecylthiomethyl)-6-methylphenol,2,4-bis(phenylthiomethyl)-3-methyl-6-tert-butylphenol, and the like, and2,4-bis(n-octylthiomethyl)-6-methylphenol is most preferred.

Furthermore, in the block copolymer composition of the presentinvention, it is essential that the composition contains at least onephenolic stabilizer (c) selected from phenolic compounds represented bythe above formulas (II)-(V). Here, R₆ in the formulas (II)-(V) isrepresented by the following formula (VI):

R₇ is an alkyl group of 2-22 carbon atoms, and R₈-R₁₂ are a hydrogenatom or an alkyl group of 1-6 carbon atoms, with a proviso that two ormore of R₈-R₁₂ are alkyl groups.

If the amount of the phenolic stabilizer (c) represented by the formulas(II)-(V) is less than 0.05 part by weight, the heat stabilization effectis small, and the effect obtained by using in combination with thephenolic stabilizer (b) represented by the formula (I) is also small.Furthermore, even if it is added in an amount exceeding 0.8 part byweight, there is substantially no effect on the heat stabilization, andrather coloration sometimes occurs. Moreover, addition of the stabilizerin an unnecessary amount is economically disadvantageous. Therefore, thelower limit of the amount of the phenolic stabilizer (c) is 0.05 part byweight, preferably 0.1 part by weight, and the upper limit is 0.8 partby weight, preferably 0.6 part by weight.

Examples of the phenolic stabilizers (c) represented by the formulas(II)-(V) are shown below.

Examples of the compounds represented by the formula (II) aren-octadecyl-3-(3′,5′-di-tert-butyl-4′-hydroxyphenyl) propionate and thelike.

Examples of the compounds represented by the formula (III) aretetrakis-[methylene-3-(3′,5′-di-tert-butyl-4′-hydroxyphenyl)propionate]-methane and the like.

Examples of the compounds represented by the formula (IV) are1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene andthe like.

Examples of the compounds represented by the formula (V) are2,6-di-tert-butyl-4-methylphenol, 2,6-di-tert-butyl-4-ethylphenol, andthe like.

As especially preferred block copolymer compositions in the presentinvention, mention may be made of compositions which comprise 100 partsby weight of the above-mentioned block copolymer, 0.055-0.25 part byweight of the phenolic stabilizer (b) represented by the formula (I),and 0.1-0.5 part by weight of the phenolic stabilizer (c) represented bythe formulas (II)-(V), and, among them, especially preferred are thosewhich contain in combination the phenolic stabilizer (b) represented bythe formula (I) and the phenolic stabilizer (c) represented by theformula (II).

Moreover, most preferably, the blending ratio (b)/(c) of the phenolicstabilizer (b) represented by the formula (I) and the phenolicstabilizer (c) represented by the formulas (II)-(V) is in the range of0.2-1.5. In the present invention, the total amount of the phenolicstabilizers (b) and (c) is preferably less than 1.4 part by weight, morepreferably not more than 1.0 part by weight.

The composition of the present invention comprises essentially the blockcopolymer (a), the phenolic stabilizer (b) represented by the formula(I) and the phenolic stabilizer (c) represented by the formulas(II)-(V), and, if necessary, a phenolic compound other than (I)-(V) mayfurther be added as a stabilizer. Examples of the phenolic compoundother than those of (I)-(V) are2-tert-butyl-6-(3-tert-butyl-2-hydroxy-5-methylbenzyl)-4-methylphenylacrylate,2-[1-(2-hydroxy-3,5-di-tert-pentylphenyl)-ethyl]-4,6-di-tert-pentylphenylacrylate, and the like, and these are suitably usable for improving heatstability under high shearing. When the phenolic compound other than(I)-(V) are used, the total amount of the phenolic stabilizers (b) and(c) and the phenolic compound other than (I)-(V) is preferably less than1.4 part by weight, more preferably not more than 1.0 part by weight.Furthermore, the amount of the phenolic compound other than (I)-(V) ispreferably 0.05-0.4 part by weight, more preferably 0.1-0.3 part byweight.

It is not necessary that the block copolymer composition of the presentinvention contains phosphorus stabilizers. The phosphorus stabilizershave hydrolytic properties and show substantially no such a high effectto improve heat stability as in the present invention.

If necessary, the composition of the present invention may contain atleast one compound selected from ultraviolet absorbers such asbenzotriazole compounds and light stabilizers such as hindered aminecompounds.

As examples of the benzotriazole compounds, mention may be made of2-(2′-hydroxy-5′-methylphenyl)benzotriazole,2-(2′-hydroxy-5′-tert-octylphenyl)benzotriazole,2-(2′-hydroxy-3′,5′-di-tert-butylphenyl)benzotriazole,2-(2′-hydroxy-3′,5′-di-tert-butylphenyl)-5-chlorobenzotriazole,2-(2′-hydroxy-3′-tert-butyl-5′-methylphenyl)-5-chlorobenzotriazole, andthe like.

As examples of the hindered amine compounds, mention may be made ofbis(2,2,6,6-tetramethyl-4-piperidyl) sebacate, succinic aciddimethyl-1-(2-hydroxyethyl)-4-hydroxy-2,2,6,6-tetramethylpiperidinepolycondensate,poly[(6-(1,1,3,3-tetramethylbutyl)imino-1,3,5-triazine-2,4-diyl][2,2,6,6-tetramethyl-4-piperidyl)imino]hexamethylene[[2,2,6,6-tetramethyl-4-piperidyl]imino]], and the like.

The light resistance of the composition of the present invention can befurther improved by adding these benzotriazole compounds and hinderedamine compounds.

The composition of the present invention can be obtained by polymerizingthe monoalkenyl aromatic compound and the conjugated diene compound inaccordance with the above-mentioned method, deactivating the resultingsolution of the block copolymer (a) with a suitable deactivating agentsuch as water, alcohol, acid, or the like, adding to the solution thetotal of a given amount of the phenolic stabilizer (b) represented bythe formula (I) and a given amount of the phenolic stabilizer (c)represented by the formulas (II)-(V) or adding directly to the solutionbefore deactivation the total of the phenolic stabilizers (b) and (c) touniformly disperse the stabilizers, and then removing the solvent bysteam stripping, heated roll, or the like.

Alternatively, the composition of the present invention can also beobtained by a method which comprises adding a part of the phenolicstabilizer (b) and a part of the phenolic stabilizer (c) to the abovesolution of the block copolymer (a), preparing a solid block copolymercomposition by the above method, and then adding the remainder of thephenolic stabilizers thereto by a kneading machine such as roll, Banburymixer, kneader, extruder, or the like.

The method of addition of the stabilizers is not particularly limited,and there may be employed any other methods, and suitable methods can beemployed depending on circumstances. The same can be applied to themethod of addition of phenolic stabilizers other than the stabilizers(b) and (c), ultraviolet absorbers and light stabilizers.

The block copolymer composition of the present invention can be used asa blend with polystyrene resins such as polystyrene, impact resistantpolystyrene and the like, ABS resins, engineering resins and the like,and can also be used as a blend with a polyolefin resin such aspolyethylene, polypropylene or the like. Furthermore, the blockcopolymer composition can be suitably used as a substrate for hot-meltadhesives by adding thereto a tackifier or an oil, and, further, may beblended with straight asphalt, blown asphalt or the like.

As far as the object of the present invention is not damaged, otheradditives such as softening agent, reinforcing agent, flame-retardant,foaming agent, plasticizer, coloring agent, and the like can be furtheradded to the block copolymer composition of the present invention.

EXAMPLES

The present invention will be explained in more detail by the followingexamples and comparative examples, which show the excellent effectsobtained by the specific construction of the present invention andshould not be construed as limiting the scope of the invention in anymanner. The various measurements are conducted in accordance with thefollowing methods.

1) Total Styrene Content in the Block Copolymer:

This was calculated from absorption intensity at 262 nm using anultraviolet spectrophotometer (Hitachi UV200).

2) Number Average Molecular Weight of the Block Copolymer:

The number average molecular weight was obtained from chromatogram ofGPC (apparatus: manufactured by Waters Co., Ltd.; column: combination ofthree columns of ZORBAXPSM 1000-S (two columns) and PSM 60-S (onecolumn) manufactured by Du Pont de Nemours, E.I. Co.; solvent:tetrahydrofuran; measuring conditions: temperature 35° C., flow rate 0.7ml/min, sample concentration 0.1% by weight, introduction amount: 50μl). The value of the number average molecular weight is a conversionvalue from a calibration curve made using a standard polystyrene(manufactured by Waters Co., Ltd.; molecular weight: 1.75×10⁶, 4.1×10⁵,1.12×10⁵, 3.5×10⁴, 8.5×10³).

Reference Example

<Preparation of Block Copolymer>

The block copolymers used in the examples of the present invention wereprepared in the following manner.

A stainless steel reaction vessel of 40 L equipped with a jacket and astirrer was subjected to sufficient replacement with nitrogen, andtherein were charged 17,600 g of cyclohexane, 5.3 g of tetrahydrofuranand 480 g of styrene (referred to as “first styrene”), followed bypassing warm water through the jacket to set the temperature of thecontent at about 65° C. Thereafter, a solution of n-butyllithium incyclohexane (pure component: 2.6 g) was added thereto to initiatepolymerization of the first styrene. After lapse of 4 minutes fromnearly complete polymerization of the first styrene, 2240 g of butadiene(1,3-butadiene) was added and continuously polymerization of butadienewas carried out. After the butadiene was nearly completely polymerized,480 g of styrene (referred to as “second styrene”) was charged andcontinuously polymerization was carried out. After completion of thepolymerization of the second styrene, water was added in an amount of 3mols per 1 mol of n-butyllithium used. After the charging of the firststyrene, the reaction system was continuously stirred by the stirrer.The resulting block copolymer had a styrene content of 30% by weight anda number average molecular weight of 105,000.

As the stabilizers, the following were used.

AO-1: 2,4-Bis(n-octylthiomethyl)-6-methylphenol

AO-2: n-Octadecyl-3-(3′,5′-di-tert-butyl-4′-hydroxyphenyl) propionate

AO-3: Tetrakis-[methylene-3-(3′,5′-di-tert-butyl-4′-hydroxyphenyl)propionate]-methane

AO-4:1,3,5-Trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene

AO-5: 2,6-Di-tert-butyl-4-methylphenol

AO-6:2-Tert-butyl-6-(3-tert-butyl-2-hydroxy-5-methylbenzyl)-4-methylphenylacrylate

AO-7: Tris(nonylphenyl) phosphite

Examples 1-6 and Comparative Examples 1-5 and 8

Each of the phenolic stabilizers (AO-1)−(AO-6) was added in a givenamount to the block copolymer solution shown in Reference Example withthe composition shown in Table 1, and the solvent was removed by steamstripping, followed by dehydration and then drying by a heated roll(110° C.) Furthermore, in Comparative Examples 3-5, after the drying,the phosphorus stabilizer (AO-7) was added in a given amount on theheated roll. Thus, samples of the block copolymer compositions ofExamples 1-6 and Comparative Examples 1-5 and 8 were prepared.

These samples were subjected to Labo plastmill kneading test, and theresulting gelation peak (torque peak) time is shown in Table 1.

From the results shown in Table 1, it can be seen that the blockcopolymer compositions containing the specific phenolic stabilizers (b)and (c) of the present invention in combination had markedly excellentgelling inhibition effect. Furthermore, the compositions containing thephosphorus stabilizer could not be sufficiently inhibited from gelation.

Comparative Examples 6, 7 and 9

Each of the phenolic stabilizers (AO-1), (AO-2) and (AO-3) was added ina given amount to the block copolymer solution shown in ReferenceExample with the composition given in Table 2, and the solvent wasremoved by steam stripping, followed by dehydration and then drying by aheated roll (110° C.) to obtain block copolymer compositions ofComparative Examples 6, 7 and 9.

Samples of the compositions of Examples 1, 2 and 4, and ComparativeExamples 3 and 6-9 were subjected to heating test. A part (5 g) of thesample was charged in a cylindrical glass sample bottle of 30 cc ininternal volume, and the top was covered with an aluminum foil. Then,this bottle was left to stand at 180° C. in a Geer oven (model GPHH-100manufactured by Tabai Espec Co., Ltd.), and change of color with time ofthe sample after heating was observed and toluene-insoluble matter wasmeasured. The results are shown in Table 2.

From the results, it can be seen that the block copolymer compositionscontaining the specific phenolic stabilizers (b) and (c) of the presentinvention in combination were excellent in the balance between the colorfastness after heating and the gelling inhibition effect.

TABLE 1 Comp. Comp. Comp. Comp. Comp. Comp. Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex.5 Ex. 6 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 8 Amount of Stabilizer(Note 1) AO-1 0.07 0.07 0.07 0.1 0.15 0.08 0 0.07 0 0 0 0.04 AO-2 0.2 00 0.25 0.3 0.2 0 0 0.2 0 0 0.5 AO-3 0 0.2 0 0 0 0 0.2 0 0 0 0 0 AO-4 0 00.2 0 0 0 0 0 0 0.2 0 0 AO-5 0 0 0 0 0 0 0 0 0 0 0.6 0 AO-6 0 0 0 0 00.2 0 0 0 0 0 0 AO-7 0 0 0 0 0 0 0 0 0.5 0.5 0.5 0 Labo.plastmillkneading test (Note 2) (Condition I) 16 13 13 23 30 22 4 11 10 9 13 12Gelation peak time (minute) (Condition II) 30 23 24 41 56 49 6 19 17 1518 18 Gelation peak time (minute) (Note 1) Amount of the stabilizer(part by weight) is based on 100 parts by weight of the block copolymer.(Note 2) Labo.plastmill kneading conditions (kneading machine; 50R150manufactured by Toyoseiki Co., Ltd.) 1. Condition I Amount of sample: 50g, Kneading conditions: After the sample was kneaded under pre-heatingat 190° C. for 3 minutes at 10 rpm, the measurement was conducted withincreasing the number of revolution to 120 rpm. 2. Condition II The samemethod as of Condition 1 was carried out in nitrogen atmosphere.

TABLE 2 Comp. Comp. Comp. Comp. Comp. Ex. 1 Ex. 2 Ex. 4 Ex. 3 Ex. 6 Ex.7 Ex. 8 Ex. 9 Amount of stabilizer (Note 1) AO-1 0.07 0.07 0.1 0 0.070.6 0.04 1.0 AO-2 0.2 0 0.25 0.2 0 0.2 0.5 0 AO-3 0 0.2 0 0 1.5 0 0 0AO-7 0 0 0 0.5 0 0 0 0 Heating test at 180° C. by Geer oven (Note 3)Color after 2 hours ⊚ ⊚ ⊚ ◯ Δ ◯ ◯ ◯ Color after 5 hours ◯ ◯ ◯ ◯˜Δ X Δ◯˜Δ Δ Color after 10 hours ◯˜Δ Δ Δ Δ˜X XX X Δ˜X X Toluene-insoluble 4251 31 81 18 16 64 20 matter after 10 hours (%) (Note 3) 1. Judgementafter heating ⊚: Colorless (white) or substantially no change ◯: Lightyellow˜yellow Δ: Light brown X: Brown XX: Dark brown 2.Toluene-insoluble matter (wt %) One gram of the composition afterheating was dissolved in 100 g of toluene, the solution was filteredthrough a wire gauze of 100 mesh, and the residue on the wire gauze wasdried and calculated as toluene-insoluble matter.

Industrial Applicability

As mentioned above, the block copolymer composition of the presentinvention shows excellent heat stability even under heating at hightemperatures, is high in the effect of being inhibited from formation ofgel-like material and is excellent in color fastness. Thus, the blockcopolymer composition of the present invention can solve the problems onheat stability in conventional block copolymer compositions and becomespossible to sufficiently exhibit the excellent elasticity, adhesion,impact resistance and the like which are possessed by block copolymerscomprising monoalkenyl aromatic compounds and conjugated dienecompounds. Therefore, the composition can be utilized in various fieldsof footwear, plastics modification, asphalt, adhesives, food packagingcontainers, and others.

What is claimed is:
 1. A block copolymer composition which comprises (a)a block copolymer comprising a polymer block segment mainly composed ofa monoalkenyl aromatic compound and a polymer block segment mainlycomposed of a conjugated diene compound, the content of the monoalkenylaromatic compound being 5-95% by weight based on the total weight of theblock copolymer, (b) a phenolic stabilizer represented by the followingformula (I):

(wherein R₁ and R₃ are —CH₂—S—R₅ in which R₅ represents an alkyl groupof 1-18 carbon atoms, R₂ represents a hydrogen atom or a methyl group,and R₄ represents an alkyl group of 1-8 carbon atoms or a cycloalkylgroup of 5-12 carbon atoms), and (c) at least one phenolic stabilizerselected from phenolic compounds represented by the following formulas,(II)-(V):

(wherein R₆ is represented by the following formula (VI):

R₇ represents an alkyl group of 2-22 carbon atoms, and R₈-R₁₂ eachrepresent a hydrogen atom or an alkyl group of 1-6 carbon atoms, with aproviso that two or more of R₈-R₁₂ are alkyl groups), the content of thephenolic stabilizer (b) being more than 0.05 part by weight and lessthan 0.6 part by weight and that of the phenolic stabilizer (c) beingnot less than 0.05 part by weight and not more than 0.8 part by weightbased on 100 parts by weight of the block copolymer (a).
 2. A blockcopolymer composition according to claim 1, wherein the component (a) isa block copolymer shown by the formula: (A-B)_(n), (A-B)_(n)A or(B-A)_(n)B (wherein A is a polymer block segments mainly composed ofmonoalkenyl aromatic compound, B is a polymer block segment mainlycomposed of conjugated diene compound, and n is an integer of 1 ormore).
 3. A block copolymer composition according to claim 1, whereinthe component (a) is a block copolymer shown by the formula:[(A-B)_(n)]_(m)-X, [(A-B)_(n)A]_(m)-X or [(B-A)_(n)B]_(m)-X (wherein Ais a polymer block segment mainly composed of monoalkenyl aromaticcompound, B is a polymer block segment mainly composed of conjugateddiene compound, n is an integer of 1 or more, m is an integer of 3 ormore, and X represents a residue of a trifunctional or higher functionalcoupling agent or a residue of a trifunctional or higher polyfunctionalorganolithium compound).
 4. A block copolymer composition according toany one of claims 1-3, wherein the block copolymer (a) has a numberaverage molecular weight of 20,000-800,000, and the content of themonoalkenyl aromatic compound is 5-60% by weight based on the totalweight of the block copolymer.